Synthetic ester and mineral oil dielectric fluids with increased stability

ABSTRACT

A dielectric fluid is provided comprising an oil and one or more compounds selected from the group consisting of phosphite compounds. It has been discovered that addition of one or more compounds selected from the group consisting of phosphite compounds to dielectric fluids comprising oil impart a stabilizing effect that reduces, inhibits or prevents formation of stray gases in the dielectric fluid during ordinary use.

FIELD

In one aspect, the present invention relates to dielectric fluidcompositions, including insulating oils, for use in electricaldistribution and power equipment, including transformers, switchinggear, and electric cables.

BACKGROUND

Dielectric (or insulating) fluids used in electrical distribution andpower equipment—including transformers, switching gear and electriccables—perform two important functions. These fluids act as anelectrical insulating medium, i.e., exhibit dielectric strength, andthey transport generated heat away from the equipment, i.e., act as acooling medium. When used in a transformer, for example, dielectricfluids transport heat from the windings and core of the transformer orconnected circuits to cooling surfaces. Apart from possessing dielectricstrength and cooling capacity, an ideal dielectric fluid for electricalequipment also exhibits little or no detrimental impact on theenvironment, is compatible with materials used to construct theequipment, and is relatively nonflammable.

There are a number of specific functional properties characteristic ofdielectric oils. An oil's dielectric breakdown, or dielectric strength,provides an indication of its ability to resist electrical breakdown andis measured as the minimum voltage required to cause arcing between twoelectrodes at a specified gap submerged in the oil. The impulsedielectric breakdown voltage provides an indication of an oil's abilityto resist electrical breakdown under transient voltage stresses such aslightning and power surges. The dissipation factor of an oil is ameasure of the dielectric losses in the oil; a low dissipation factorindicates low dielectric loss and a low concentration of soluble, polarcontaminants. The gassing tendency of an oil measures the oil's tendencyto evolve or absorb gas under conditions where partial discharge ispresent. Likewise, stray gassing may occur as the result of thermalstress of dielectric oils (such as transformer oils), resulting in therelease of hydrogen, methane, ethane, ethylene, etc.

Because one function of a dielectric fluid is to carry and dissipateheat, factors that significantly affect the relative ability of thefluid to function as a dielectric coolant include viscosity, specificheat, thermal conductivity, and the coefficient of expansion. The valuesof these properties, particularly in the range of operating temperaturesfor the equipment at full rating, must be weighed in the selection ofsuitable dielectric fluids for specific applications.

In addition to the foregoing properties that affect heat transfer, adielectric fluid should have a relatively high dielectric strength, lowdissipation factor, a dielectric constant that is compatible with thesolid dielectric, a low gassing tendency, and it must be compatible withthe electrical equipment materials to which it is exposed. Control ofstray gassing prevents buildup of explosive gases in the head space ofelectrical equipment.

A dielectric fluid for use in electrical equipment comprising avegetable oil or vegetable oil blend and comprising one or moreantioxidant compounds is described in U.S. Pat. No. 7,651,641 toCorkran, et al.

SUMMARY

A typical practice in preparation of dielectric fluids to reduce theeffects of oxidative degradation is to add a di-tertbutylphenol-basedantioxidant. These antioxidants act by extracting a hydrogen radicalfrom the peroxide formed during oxidation, and sequestering the radical.The resulting quinone methides and stilbenquinones are highly colored,which is considered detrimental in certain dielectric fluid applicationsor in situations where color interferes with visualization of oilquality. In addition, passivators, such as aryl-triazines, have beenadded to dielectric fluids to reduce the catalysis of oxidativedegradation by dissolved metals and metal surfaces, thus prolonging thelife of the antioxidant.

Oils used as dielectric fluids, e.g. mineral oils, synthetic esters, andin particular bio-sourced oils, have limitations of stability when usedas dielectric fluids. Thermal degradation is evidenced by generation ofstray gases selected from hydrogen, methane, ethane, and ethylene. Straygassing is measured in accordance with ASTM D3612-02, Method C.Oxidative degradation in particular increases the hydrogen and ethaneconcentrations of thermal degradation, and is often accompanied bygeneration of organic acids, alcohols and peroxides. Ionizingdegradation from partial discharge (leakage of electrons) is evidencedby hydrogen and methane, and arching and static discharge is accompaniedby generation of hydrogen and acetylene.

It has been discovered that addition of a phosphite component comprisingone or more phosphite compounds to dielectric fluids comprising oilsimparts a stabilizing effect that reduces, inhibits or preventsformation of stray gases in the dielectric fluid during ordinary use.While not being bound by theory, it is believed that addition of one ormore compounds selected from the group consisting of phosphite compoundsto dielectric fluids imparts a stabilizing effect prior to formation ofperoxides, thereby advantageously preventing formation of gases.

In an aspect, a dielectric fluid is provided comprising an oil and oneor more compounds selected from the group consisting of phosphitecompounds. In an aspect, a dielectric fluid is provided comprising anoil and one or more compounds selected from the group consisting ofphosphite compounds, and further comprises a non-phosphite antioxidantcomponent selected from one or more non-phosphite antioxidant compounds.

In an aspect, a dielectric fluid formulated for use in an electricaldistribution or power device is provided, the dielectric fluidcomprising an oil and one or more compounds selected from the groupconsisting of phosphite compounds.

In an aspect, a method of insulating an electrical distribution or powerdevice is provided, comprising incorporating a dielectric fluid asdescribed herein in the electrical distribution or power device.

In an aspect, an electrical distribution or power device is provided,comprising a dielectric fluid as described herein.

DETAILED DESCRIPTION

The aspects of the present invention described below are not intended tobe exhaustive or to limit the invention to the precise forms disclosedin the following detailed description. Rather a purpose of the aspectschosen and described is by way of illustration or example, so that theappreciation and understanding by others skilled in the art of thegeneral principles and practices of the present invention can befacilitated.

In an aspect, the dielectric fluid comprises an oil selected from thegroup consisting of a bio-sourced oil, a synthetic ester oil, mineraloil, and mixtures thereof.

In an aspect, the dielectric fluid comprises a bio-sourced oil. Forpurposes of the present disclosure, a bio-sourced oil is an oil derivedfrom vegetable or animal sources. In an aspect, the bio-sourced oil is arefined, bleached and deodorized (“RBD”) oil. In an aspect, thedielectric fluid comprises at least 75% by weight of a bio-sourced oil.In an aspect, the dielectric fluid comprises at least 85% by weight of abio-sourced oil. In an aspect, the dielectric fluid comprises at least90% by weight of a bio-sourced oil. In an aspect, the dielectric fluidcomprises at least 95% by weight of a bio-sourced oil. In an aspect, thedielectric fluid comprises at least 98% by weight of a bio-sourced oil.In an aspect, the only oil in the dielectric fluid is a bio-sourced oil.

Bio-sourced oils are particularly desirable for use in the presentdielectric fluid, because they are derived from renewable resources andare generally readily biodegradable. In an aspect, bio-sourced oils havethe additional property of increasing paper stability in transformerapplications. Bio-sourced oils bring the benefit of high flash and firepoint properties, low ignitability, and low fire propagation unlikemineral oils. The flash, fire point, and ignitability of syntheticesters are highly dependent upon composition. Under certain conditions,mineral oils are subject to explosions and fire propagation, acting likegasoline around ignition sources. Bio-sourced oils comprisingunsaturation provide beneficial flow properties, with decreasingviscosity of the oil correlating to increased unsaturation.

In an aspect, the oil in the dielectric fluid is a natural bio-sourcedoil, meaning that it is obtained from the vegetable or animal sourcethat has not been modified by reactive chemistry, for example, bytransesterification or formation of oil derivative products. Forclarity, it is understood that a vegetable or animal oil that ismodified by interesterification (i.e., redistribution of the fatty acidmoieties present in a triglyceride oil over its glycerol moieties) isconsidered to be a natural bio-sourced oil. Additionally, it isunderstood that a vegetable or animal oil that is obtained by extractionis considered to be a natural bio-sourced oil.

In an aspect, the dielectric fluid comprises a vegetable oil. In anaspect, the dielectric fluid comprises a vegetable oil, selected fromthe group consisting of castor, coconut, corn, cottonseed, crambie,flaxseed, jojoba, kukui nut, lesquerella, linseed, olive, palm, peanut,pine nut, rapeseed, safflower, sunflower, soybean, and veronica oil, andmixtures thereof. In an aspect, the only oil in the dielectric fluid isa vegetable oil. In an aspect, the only oil in the dielectric fluid is avegetable oil selected from the group consisting of castor, coconut,corn, cottonseed, crambie, flaxseed, jojoba, kukui nut, lesquerella,linseed, olive, palm, peanut, pine nut, rapeseed, safflower, sunflower,soybean, and veronica oil, and mixtures thereof. In an aspect, the onlyoil in the dielectric fluid is a vegetable oil. In an aspect, thedielectric fluid comprising a vegetable oil may be provided acommercially available oil composition that is further modified byaddition of phosphite compounds. For example, Envirotemp FR3 is anatural ester fluid made from soybean oil and additives (di-tert-butylphenolic class of antioxidants, pour point additive, dye). Other similarfluids that can be derived from renewable sources include Midel eN(Rapeseed based). These materials may be modified by addition ofphosphite compounds to decrease stray gassing.

In an aspect, the dielectric fluid comprises a natural oil obtained frommicrobes, seaweed and like organic sources.

In an aspect, the dielectric fluid comprises an animal oil. In anaspect, the only oil in the dielectric fluid is an animal oil.Representative examples of animal oils include tallow, lard, fish oil,or chicken fat.

In an aspect, the dielectric fluid comprises a synthetic oil. In anaspect, a synthetic oil is an oil that is the product of a chemicalreaction involving formation of esters by reacting a polyol withsaturated or unsaturated linear and branched carboxylic acids; arylesters; C5-C12 saturated or unsaturated linear and branched esters; andmixtures thereof, or carrying out a chemical modification of source oilsby reactive chemistry, for example, by transesterification or formationof oil derivative products. Thus, an oil obtained from a vegetable oranimal source by chemical modification by transesterification is forpurposes of the present discussion a synthetic oil. In an aspect, thedielectric fluid comprises a synthetic oil that is prepared fromreactants that are derived only from vegetable or animal bio-sourcedoils.

In an aspect, a synthetic ester oil comprises synthetic esters of apolyol selected from glycerol, pentaerythritol, trimethylolpropane(TMP), hydroxylated fatty acids, and polyglycerols. In an aspect, thesynthetic esters are formed by reacting the polyol with compoundsselected from C5-C25 saturated or unsaturated linear and branchedcarboxylic acids; from C5-C12 saturated or unsaturated linear andbranched carboxylic acids; aryl esters; C5-C12 saturated or unsaturatedlinear and branched esters; C5-C25 saturated or unsaturated linear andbranched esters; and mixtures thereof.

In an aspect, the dielectric fluid comprises synthetic esters selectedfrom the group consisting of esters of C5 through C24 branched andlinear aliphatic carboxylic acids with pentaerythritol,dipentaerythritol, 2,2-dimethylpropanediol,2,2-dimethyl-3-isopropyl-1,3-propanediol, trimethylolpropane, glycerol,neopentyl glyxol, 2,2-dimethylol butane, trimethylol ethane, sorbitol,(C2 to C12 diols) ethylene glycol, proplylene glycol, 1,4-butanediol,and 2-methylpropanediol, and mixtures thereof.

In an aspect, the dielectric fluid comprises synthetic esters selectedfrom the group consisting of selected from the group consisting ofesters of C5 through C24 branched and linear aliphatic alcohols andacids selected from the group consisting of adipic acid, suberic acid,azelaic acid, sebacic acid, phthalic acid, oxalic acid, glycolic acid,fumaric acid, and mixtures thereof.

In an aspect, the only oil in the dielectric fluid is a synthetic oil.

In an aspect, the dielectric fluid comprises mineral oil. In an aspect,the dielectric fluid comprises a mineral oil selected from the groupconsisting of straight and branched chain aliphatic paraffinichydrocarbons, which have a molecular weight of about 220 to about 700;or from about 500 to about 700. In an aspect, the dielectric fluidcomprises a mineral oil having a fire point of from about 120° C. toabout 250° C.; or having a fire point of from about 140° C. to about200° C. In an aspect, the dielectric fluid comprises a mineral oilhaving a fire point above 200° C. In an aspect, the dielectric fluidcomprises a mineral oil selected from the group consisting of naphthenichydrocarbon oils having similar characteristics and mixtures of theaforementioned paraffinic and naphthenic hydrocarbons, such as describedin U.S. Pat. No. 4,082,866, the disclosure of which is incorporatedherein by reference. In an aspect, the only oil in the dielectric fluidis a mineral oil.

In an aspect, the dielectric fluid comprises a mixture of a bio-sourcedoil and a mineral oil. In an aspect, the dielectric fluid comprises amixture of a vegetable oil and a mineral oil. In an aspect, thedielectric fluid comprises a mixture of a synthetic ester oil and amineral oil. In an aspect, the dielectric fluid comprises a mixture of asynthetic ester oil and a bio-sourced oil. In an aspect, the dielectricfluid comprises a mixture of a synthetic ester oil and a vegetable oil.In an aspect, the dielectric fluid comprises a mixture of a syntheticester oil, a bio-sourced oil, and a mineral oil. In an aspect, thedielectric fluid comprises a mixture of a synthetic ester oil, avegetable oil, and a mineral oil.

It has been found that increased unsaturation and branching in oils istied to increased stray gassing. In oils comprising significant amountsof unsaturation and branching, addition of phosphite compounds todecrease stray gassing becomes more important. It is noted that oilsthat have a relatively low amount or no unsaturation, (e.g. having aIodine Value of less than 50) strongly benefit by incorporation ofphosphite compounds as described herein. However, oils that have arelatively high amount of unsaturation even more significantly benefitfrom addition of phosphite compounds to decrease stray gassing. In anaspect, the dielectric fluid comprises an oil having an IV of from 50 to200. In an aspect, the dielectric fluid comprises an oil having an IV offrom 80 to 200. In an aspect, the dielectric fluid comprises an oilhaving an IV of from 100 to 200. In an aspect, the dielectric fluidcomprises an oil having an IV of from 110 to 200.

For purposes of the present disclosure, “Iodine Value” (IV) is definedas the number of grams of iodine that will react with 100 grams ofmaterial being measured. Iodine value is a measure of the unsaturation(carbon-carbon double bonds and carbon-carbon triple bonds) present in amaterial. Iodine Value is reported in units of grams iodine (I₂) per 100grams material and is determined using the procedure of AOCS Cd Id-92.

In an aspect, the dielectric fluid is free of silicone compounds, or isfree of phospholipids, or is free of pigments, or is free of lecithin,or is free of fatty acids, or is free of mono- and di-glycerides, or isfree of acids, or is free of alcohols, or is free of colored impurities,or is free of sulfur compounds, or is free of cresols, or is free ofpolyaromatic hydrocarbons, or is free of acids, or is free ofhalogenated compounds, or is free of amines. In an aspect, thedielectric fluid comprises a natural bio-sourced oil and is free ofphospholipids, or is free of pigments, or is free of lecithin, or isfree of fatty acids, or is free of mono- and di-glycerides. In anaspect, the dielectric fluid comprises a synthetic ester oil and is freeof acids, or is free of alcohols, or is free of colored impurities. Inan aspect, the dielectric fluid comprises a mineral oil and is of sulfurcompounds, or is free of cresols, or is free of polyaromatichydrocarbons, or is free of acids, or is free of halogenated compounds,or is free of amines.

In an aspect, the dielectric fluid comprises an oil that is highlypurified. For purposes of the present disclosure, an oil is “highlypurified” if the oil is treated on a clay medium (such as silicates,aluminates, and the like) to remove polar compounds and impurities,followed by filtration to substantially remove particles that would beretained by a 1 micron filter. In an aspect, the dielectric fluidcomprises a bio-sourced oil that is highly purified.

It has been discovered that it is advantageous when selecting the oil tobe used in the dielectric fluid, that the oil has a low initial peroxidevalue so that undesirable side reactions and gas evolution may beavoided from the start. It is preferred that the peroxide values intransformer oils be kept low by degassing and maintaining an inert(nitrogen blanketed) headspace, so that the additives are spent on thetargeted oil maintenance during use, and are not spent on correcting oilconditions that accrue prior to their introduction into the application.Over time of exposure of the dielectric fluid to atmosphere or oxidizingconditions, the peroxide value of the oil in the dielectric fluid mayincrease, for example, from a very low initial peroxide value of lessthan about 1 to a higher peroxide value of about 8 or 10 or even higher.It has been discovered that phosphite compounds are particularlyeffective in inhibiting gas generation in dielectric fluids where theoil has an initial peroxide value of less than 5, or where the oil hasan initial peroxide value of less than 3, or where the oil has aninitial peroxide value of less than 2, or where the oil has an initialperoxide value of less than 1. In an aspect, the oil used in thedielectric fluid has an initial peroxide value of from about 0.01 to 5,or has an initial peroxide value of from about 0.01 to 3, or has aninitial peroxide value of from about 0.01 to 2, or has an initialperoxide value of from about 0.01 to 1, or has an initial peroxide valueof from about 0.1 to 1. For purposes of the present disclosure,“peroxide value” is determined by AOCS Method Cd 8b-90. It should benoted, however, that dielectric fluids having a high initial peroxidevalue exhibit reduction in stray gassing by addition of phosphitecompounds as described herein.

In an aspect, the dielectric fluid comprises one or more compoundsselected from the group consisting of phosphite compounds.

In an aspect, the phosphite component is present in an amount sufficientto reduce the hydrogen (H₂) gassing of the dielectric fluid asdetermined by dissolved gas analysis (ASTM D3612-02, Method C) by atleast 60% as compared to a like dielectric fluid composition that doesnot contain a phosphite component. In an aspect, the phosphite componentis present in an amount sufficient to reduce the H₂ gassing of thedielectric fluid as determined by dissolved gas analysis by at least 70%as compared to a like dielectric fluid composition that does not containa phosphite component. In an aspect, the phosphite component is presentin an amount sufficient to reduce the H₂ gassing of the dielectric fluidas determined by dissolved gas analysis by at least 80% as compared to alike dielectric fluid composition that does not contain a phosphitecomponent.

In an aspect, the phosphite component is present in an amount sufficientto reduce the ethane gassing of the dielectric fluid as determined bydissolved gas analysis (ASTM D3612-02, Method C) by at least 60% ascompared to a like dielectric fluid composition that does not contain aphosphite component. In an aspect, the phosphite component is present inan amount sufficient to reduce the ethane gassing of the dielectricfluid as determined by dissolved gas analysis by at least 70% ascompared to a like dielectric fluid composition that does not contain aphosphite component. In an aspect, the phosphite component is present inan amount sufficient to reduce the ethane gassing of the dielectricfluid as determined by dissolved gas analysis by at least 80% ascompared to a like dielectric fluid composition that does not contain aphosphite component.

In an aspect, the phosphite component is present in an amount sufficientto reduce the methane gassing of the dielectric fluid as determined bydissolved gas analysis (ASTM D3612-02, Method C) by at least 60% ascompared to a like dielectric fluid composition that does not contain aphosphite component. In an aspect, the phosphite component is present inan amount sufficient to reduce the methane gassing of the dielectricfluid as determined by dissolved gas analysis by at least 70% ascompared to a like dielectric fluid composition that does not contain aphosphite component. In an aspect, the phosphite component is present inan amount sufficient to reduce the methane gassing of the dielectricfluid as determined by dissolved gas analysis by at least 80% ascompared to a like dielectric fluid composition that does not contain aphosphite component.

In an aspect, the phosphite component is present in an amount sufficientto reduce the ethylene gassing of the dielectric fluid as determined bydissolved gas analysis (ASTM D3612-02, Method C) by at least 60% ascompared to a like dielectric fluid composition that does not contain aphosphite component. In an aspect, the phosphite component is present inan amount sufficient to reduce the ethylene gassing of the dielectricfluid as determined by dissolved gas analysis by at least 70% ascompared to a like dielectric fluid composition that does not contain aphosphite component. In an aspect, the phosphite component is present inan amount sufficient to reduce the ethylene gassing of the dielectricfluid as determined by dissolved gas analysis by at least 80% ascompared to a like dielectric fluid composition that does not contain aphosphite component.

In an aspect, the phosphite component is present in an amount sufficientto reduce the hydrogen gassing of the dielectric fluid as determined bydissolved gas analysis (ASTM D3612-02, Method C) by at least 60%, andadditionally the ethane gassing of the dielectric fluid as determined bydissolved gas analysis (ASTM D3612-02, Method C) by at least 60% ascompared to a like dielectric fluid composition that does not contain aphosphite component. In an aspect, the phosphite component is present inan amount sufficient to reduce the hydrogen gassing of the dielectricfluid as determined by dissolved gas analysis by at least 70%, andadditionally the ethane gassing of the dielectric fluid as determined bydissolved gas analysis by at least 70% as compared to a like dielectricfluid composition that does not contain a phosphite component. In anaspect, the phosphite component is present in an amount sufficient toreduce the hydrogen gassing of the dielectric fluid as determined bydissolved gas analysis by at least 80%, and additionally the ethanegassing of the dielectric fluid as determined by dissolved gas analysisby at least 80% as compared to a like dielectric fluid composition thatdoes not contain a phosphite component.

In an aspect, the phosphite component is present in an amount of from0.05 to the limit of solubility in the dielectric fluid. In an aspect,the phosphite component is present in an amount of from 0.1 to the limitof solubility in the dielectric fluid. In an aspect, the phosphitecomponent is present in an amount of from 0.05 to 4% wt. In an aspect,the phosphite component is present in an amount of from 0.05 to 3% wt.In an aspect, the phosphite component is present in an amount of from0.05 to 2% wt. In an aspect, the phosphite component is present in anamount of from 0.05 to 1.5% wt. In an aspect, the phosphite component ispresent in an amount of from 0.05 to 1% wt. In an aspect, the phosphitecomponent is present in an amount of from 0.05 to 0.5% wt. In an aspect,the phosphite component is present in an amount of from 0.1 to 4% wt. Inan aspect, the phosphite component is present in an amount of from 0.1to 3% wt. In an aspect, the phosphite component is present in an amountof from 0.1 to 2% wt. In an aspect, the phosphite component is presentin an amount of from 0.1 to 1.5% wt. In an aspect, the phosphitecomponent is present in an amount of from 0.1 to 1% wt. In an aspect,the phosphite component is present in an amount of from 0.1 to 0.5% wt.

In an aspect, the dielectric fluid comprises one or more compoundsselected from the group consisting of phosphite compounds that are WaterStable. For purposes of the present disclosure, a phosphite compound isdefined as Water Stable if when a solid sample of the phosphite compoundis placed in an 85% relative humidity chamber at 60° C. and sampled fordetermination of % hydrolysis as a function of time, the samplehydrolyzes no more than 30% in 80 minutes.

In an aspect, the dielectric fluid comprises one or more compoundsselected from the group consisting of phosphite compounds selected fromthe group consisting of phosphite esters, triarylphosphites,trialkylphosphites, cyclic phosphites, bis-arylphosphite pentaerythritolcyclic esters, and the like.

In an aspect, the phosphite component is selected from the groupconsisting of from phosphite compounds having one to three aryloxygroups. In an aspect, the phosphite component is selected from arylphosphite compounds. In an aspect, the phosphite component is selectedfrom triaryl phosphite compounds. In an aspect, the phosphite componentis selected from the group consisting of from phosphite compounds thatare cyclic esters and bis-arylphosphite pentaerythritol cyclic esters.In an aspect, the phosphite component is selected from the groupconsisting of cyclic aryl phosphites, cyclic alkyl-aryl phosphites, arylcyclic phenoxy phosphites, bis aryl phosphites, alkyl aryl phosphites,and mixtures thereof.

In an aspect, the phosphite component is selected from the groupconsisting of tris-(2,4-di-tert-butylphenyl)phosphite (commerciallyavailable, for example, as Irgafos 168); bis (2,4-dicumylphenylpentaerythritol diphosphite (commercially available, for example, asDoverphos S-9228); tris-nonylphenylphosphite (commercially available,for example, as Adela ADK Stabilizer 1178 or Doverphos 4);1,3,7,9-tetratert-butyl-11-(2-ethylhexoxy)-5H-benzo[d][1,3,2]benzodioxaphosphocine(commercially available, for example, as Amfine HP-10);3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane(commercially available, for example, as Amfine PEP-36A);bis(2,4-di-tert-butylphenol)pentaerythritol diphosphite commerciallyavailable as Irgafos 126); 4,4′-Isopropylidenediphenol C12-15 alcoholphosphite (commercially available, for example, as Amfine 1500);3,9-diphenoxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane;3,9-Bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane(commercially available, for example, as Amfine PEP-8); triphenylphosphite (commercially available, for example, as Amfine TPP orDoverphos 10); isodecyl diphenyl phosphite (commercially available, forexample, as Adela ADK Stabilizer 135A or Doverphos 8); phenyl diisodecylphosphite (commercially available, for example, as Doverphos 7);diisodecyl petaerythrytol diphosphite (commercially available, forexample, as Doverphos 1220); distearyl petaerythrytol diphosphite(commercially available, for example, as Doverphos S-680); trilaurylphosphite (commercially available, for example, as Doverphos 53); alkyl(C₁₂-C₁₅) bisphenol A phosphite (commercially available, for example, asDoverphos 613); alkyl (C₁₀) bisphenol A phosphite (commerciallyavailable, for example, as Doverphos 675); 2-ethylhexyl diphenylphosphite (commercially available, for example, as Amfine C);5,5-dimethy-2-phenoxy-1,3,2-dioxaphosphorinane; methyl diphenylphosphite; and mixtures thereof.

In an aspect, the dielectric fluid comprising phosphite compoundsfurther comprises a non-phosphite antioxidant component that comprisesone or more non-phosphite antioxidant compounds. Incorporation of one ormore non-phosphite antioxidant compounds in the dielectric fluidcomprising phosphite compounds has been found to compliment and furtheraugment protection of the dielectric fluid from oxidative degradation.Additionally, incorporation of one or more non-phosphite antioxidantcompounds in the dielectric fluid comprising phosphite compounds in anaspect has been found to inhibit viscosity increase over time ascompared to like compositions that do not contain a non-phosphiteantioxidant component. It has been found that the presence of anon-phosphite antioxidant component, and particularly phenolicantioxidant compounds, in an aspect are advantageous to provideoxidative stability in compositions that are exposed to oxygen. Thus,compositions that contain both phosphite components and a non-phosphiteantioxidant component in the composition in an aspect exhibit good straygas inhibition properties and oxidation stability as determined bymeasuring of the Oxidation Induction Time (“OIT”) as measured under ASTMD6186-98 at the stated temperatures. The OIT test is carried out at anair pressure of 500+/−25 psig and an airflow rate of 100+/−10 ml/min.

It is noted that the presence of a conventional antioxidant(non-phosphite antioxidant compounds, especially phenolic antioxidants)does not prevent formation of peroxide, but instead acts to degradeperoxides after the peroxide is formed. Further, bio-sourced oils thathave air in the headspace will increase in peroxide value over time.Oxidation can be decreased by displacing oxygen atmosphere with an inertgas, such as nitrogen or argon, and by degassing the fluid. However,often the conventional antioxidant will not effectively reduce peroxidebuildup at ambient temperature. Elevated temperature is effective atincreasing the interaction between the conventional antioxidant andperoxide, but also increases the rate of thermal degradation of the oil.At approximately 120° C., the rate of peroxide degradation increases toexceed the rate of peroxide formation. In the presence of conventionalantioxidant, alcohols are the byproduct of peroxide degradation. In theabsence of antioxidant, the peroxide species degrade to form acids.

It has been observed that increased peroxide content also contributes toincreased stray gassing. However, stray gassing that arises fromdegradation through the peroxide formation and this form of degradationis significantly reduced by the use of phosphite compounds as describedherein.

When the oil used is a mineral oil, it has been found that peroxideformation and degradation of mineral oil dielectric compositions tend toaccelerate at about 120° C. For this reason, heating of a mineral oilbased dielectric composition for the purpose of controlling peroxide byinteraction with a conventional antioxidant in the composition is not apreferred method.

In an aspect, the additional non-phosphite antioxidant component isselected from are phenolic antioxidants, and in an aspect aredi-tert-butyl phenol analogues. In an aspect, the non-phosphiteantioxidant component is selected from the group consisting of butylatedhydroanisole (BHA), butylated hydrotoluene (BHT), tertiarybutylhydroquinone (TBHQ), tetrahydrobutrophenone (THBP), ascorbylpalmitate (rosemary oil), propyl gallate, and alpha-, beta- ordelta-tocopherol (vitamin E) and mixtures thereof

In an aspect, the additional non-phosphite antioxidant component isselected from the group consisting of Pentaerythritoltetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (commerciallyavailable, for example, as Iganox L101, Irganox 1010, BNX 1010);Hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate](commercially available, for example, as Irganox L109);Octadecyl-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate](commercially available, for example, as Irganox 1076); Ethylenebis(oxyethylene) bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate)(commercially available, for example, as Irganox 245);2,6-Di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol(commercially available, for example, as Irganox 565);N,N′-hexane-1,6-diylbis(3-3,5-di-tert-butyl-4-hydroxyphenylpropionamide)(commercially available, for example, as Irganox 1098);4,6-Bis(octylthiomethyl)-o-cresol (commercially available, for example,as Irganox 1520); 4,4′-methylene-bis-2,6-di-tert-butyl phenol(commercially available, for example, as Ethanox 4702); and2,6-Di-tert-butyl-4-methylphenol (BHT).

In an aspect, it has been found that the amount of phosphite componentsin the composition, the amount of non-phosphite antioxidant componentsin the composition, and the relative ratio of phosphite components tonon-phosphite antioxidant components within a particular range exhibitparticularly excellent properties in inhibition of generation of straygases and control of oxidative reduction. In an aspect, it has beenfound that incorporation of too much of the non-phosphite antioxidantcomponents relative to the amount of phosphite components may adverselyaffect inhibition of generation of stray gases.

In an aspect, the phosphite component is present in an amount of fromabout 0.05 wt % to the limit of solubility of the phosphite component inthe dielectric fluid composition, and the non-phosphite antioxidantcomponent is present in an amount such that the ratio of phosphitecomponent to non-phosphite antioxidant component is from 1 partphosphite component to from 0 to 1.2 parts of non-phosphite antioxidantcomponent.

In an aspect, the phosphite component is present in an amount of fromabout 0.2 wt % to the limit of solubility of the phosphite component inthe dielectric fluid composition, and the non-phosphite antioxidantcomponent is present in an amount such that the ratio of phosphitecomponent to non-phosphite antioxidant component is from 1 partphosphite component to from 0 to 1.2 parts of non-phosphite antioxidantcomponent.

In an aspect, the phosphite component is present in an amount of fromabout 0.2 wt % to about 1 wt %, and the non-phosphite antioxidantcomponent is present in an amount such that the ratio of phosphitecomponent to non-phosphite antioxidant component is from 1 partphosphite component to from 0 to 1.2 parts of non-phosphite antioxidantcomponent.

In an aspect, the phosphite component is present in an amount of fromabout 0.4 wt % to the limit of solubility of the phosphite component inthe dielectric fluid composition, and the non-phosphite antioxidantcomponent is present in an amount such that the ratio of phosphitecomponent to non-phosphite antioxidant component is from 1 partphosphite component to from 0 to 1.2 parts of non-phosphite antioxidantcomponent.

In an aspect, the phosphite component is present in an amount of fromabout 0.4 wt % to about 0.6 wt %, and the non-phosphite antioxidantcomponent is present in an amount such that the ratio of phosphitecomponent to non-phosphite antioxidant component is from 1 partphosphite component to from 0 to 1.2 parts of non-phosphite antioxidantcomponent.

In an aspect, the phosphite component is present in an amount of fromabout 0.05 wt % to the limit of solubility of the phosphite component inthe dielectric fluid composition, the phosphite component is present inan amount of from about 0.05 wt % to the limit of solubility of thenon-phosphite antioxidant component in the dielectric fluid composition;and further provided that the ratio of phosphite components tonon-phosphite antioxidant component is from 1 part phosphite componentto from 0 to 1.2 parts of non-phosphite antioxidant component.

In an aspect, the phosphite component is present in an amount of fromabout 0.2 wt % to the limit of solubility of the phosphite component inthe dielectric fluid composition, the phosphite component is present inan amount of from about 0.05 wt % to the limit of solubility of thenon-phosphite antioxidant component in the dielectric fluid composition;and further provided that the ratio of phosphite components tonon-phosphite antioxidant component is from 1 part phosphite componentto from 0 to 1.2 parts of non-phosphite antioxidant component.

In an aspect, the phosphite component is present in an amount of fromabout 0.2 wt % to about 1 wt, the phosphite component is present in anamount of from about 0.05 wt % to the limit of solubility of thenon-phosphite antioxidant component in the dielectric fluid composition;and further provided that the ratio of phosphite components tonon-phosphite antioxidant component is from 1 part phosphite componentto from 0 to 1.2 parts of non-phosphite antioxidant component.

In an aspect, the phosphite component is present in an amount of fromabout 0.4 wt % to the limit of solubility of the phosphite component inthe dielectric fluid composition, the phosphite component is present inan amount of from about 0.05 wt % to the limit of solubility of thenon-phosphite antioxidant component in the dielectric fluid composition;and further provided that the ratio of phosphite components tonon-phosphite antioxidant component is from 1 part phosphite componentto from 0 to 1.2 parts of non-phosphite antioxidant component.

In an aspect, the phosphite component is present in an amount of fromabout 0.4 wt % to about 0.6 wt %, the phosphite component is present inan amount of from about 0.05 wt % to the limit of solubility of thenon-phosphite antioxidant component in the dielectric fluid composition;and further provided that the ratio of phosphite components tonon-phosphite antioxidant component is from 1 part phosphite componentto from 0 to 1.2 parts of non-phosphite antioxidant component.

In an aspect, the phosphite component is present in an amount of fromabout 0.4 wt % to the limit of solubility of the phosphite component inthe dielectric fluid composition, the phosphite component is present inan amount of from about 0.2 wt % to the limit of solubility of thenon-phosphite antioxidant component in the dielectric fluid composition;and further provided that the ratio of phosphite components tonon-phosphite antioxidant component is from 1 part phosphite componentto from 0 to 1.2 parts of non-phosphite antioxidant component.

In an aspect, the phosphite component is present in an amount of fromabout 0.4 wt % to about 0.6 wt %, the phosphite component is present inan amount of from about 0.2 wt % to the limit of solubility of thenon-phosphite antioxidant component in the dielectric fluid composition;and further provided that the ratio of phosphite components tonon-phosphite antioxidant component is from 1 part phosphite componentto from 0 to 1.2 parts of non-phosphite antioxidant component.

In an aspect, the phosphite component is present in an amount of fromabout 0.4 wt % to the limit of solubility of the phosphite component inthe dielectric fluid composition, the phosphite component is present inan amount of from about 0.3 wt % to the limit of solubility of thenon-phosphite antioxidant component in the dielectric fluid composition;and further provided that the ratio of phosphite components tonon-phosphite antioxidant component is from 1 part phosphite componentto from 0 to 1.2 parts of non-phosphite antioxidant component.

In an aspect, the phosphite component is present in an amount of fromabout 0.4 wt % to about 0.6 wt %, the phosphite component is present inan amount of from about 0.3 wt % to the limit of solubility of thenon-phosphite antioxidant component in the dielectric fluid composition;and further provided that the ratio of phosphite components tonon-phosphite antioxidant component is from 1 part phosphite componentto from 0 to 1.2 parts of non-phosphite antioxidant component.

In an aspect, the dielectric fluid further comprises a metal passivator.Incorporation of a metal passivator has been found to be useful indielectric fluids, particularly for those comprising synthetic esteroils. While not being bound by theory, it is believed that metalpassivators act to reduce the catalysis of oxidative degradation bydissolved metals and metal surfaces in the environment of use of thedielectric fluids. Additionally, dielectric fluid compositions asdescribed herein that additionally comprise metal passivators have beenfound to exhibit low fluid dissipation factor values (and thereforereduced electrostatic charging tendency), even under conditions of longterm oxidative stress.

In an aspect, the metal passivator is selected from benzotriazole or itsderivatives. In an aspect, the metal passivator is selected fromN,N-bis(2-ethylhexyl)-ar-methyl-1H-Benzotriazole-1-methanamine(commercially available, for example, as Irgamet 39);N,N-bis(2-ethylhexyl)-1H-1,2,4-Triazole-1-methanamine (commerciallyavailable, for example, as Irgamet 30); 1H-Benzotriazole (commerciallyavailable, for example, as Irgamet BTZ); Methyl-1H-benzotriazole(commercially available, for example, as Irgamet TTZ);butyl-1H-benzotriazole; and2,2′-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bis-ethanol(commercially available, for example, as Irgamet 42).

In an aspect, the metal passivator is present in amount of from about0.001 to 2 wt % of the dielectric fluid. In an aspect, the metalpassivator is present in amount of from about 0.005 to 1 wt % of thedielectric fluid. In an aspect, the metal passivator is present inamount of from about 0.005 to 0.4 wt % (i.e. 50 to 4000 ppm) of thedielectric fluid.

In an aspect, when the oil of the dielectric fluid is a synthetic ester,the metal passivator is present in amount sufficient to control thedissipation value of the dielectric fluid as determined by IEC 60247(120° C.) at or below 0.10 (10%) at 164 hours of oxidative stabilitytesting as evaluated in accordance with by IEC 61125 Method C. In anaspect, when the oil of the dielectric fluid is a synthetic ester oil,the metal passivator is present in amount sufficient to control thedissipation value of the dielectric fluid as determined by IEC 60247(120° C.) at or below 0.30 (30%) at 164 hours of oxidative stabilitytesting as evaluated in accordance with by IEC 61125 Method C. In anaspect, when the oil of the dielectric fluid is a synthetic ester oil,the metal passivator is present in amount sufficient to control thedissipation value of the dielectric fluid as determined by IEC 60247(120° C.) at or below 0.50 (50%) at 164 hours of oxidative stabilitytesting as evaluated in accordance with by IEC 61125 Method C.

In an aspect, when the oil of the dielectric fluid is a synthetic ester,the metal passivator is present in amount sufficient to control thedissipation value of the dielectric fluid as determined by IEC 60247(120° C.) at or below 0.30 (30%); or at or below 0.60 (60%); or at orbelow 0.90 (90%); or at or below 1.0 (100%) at 800 hours of oxidativestability testing as evaluated in accordance with by IEC 61125 Method C.

In an aspect, when the oil of the dielectric fluid is a synthetic esteroil, the metal passivator is present in amount sufficient to control thedissipation value of the dielectric fluid as determined by IEC 60247(120° C.) at or below 0.60 (60%) at 164 hours of oxidative stabilitytesting as evaluated in accordance with by IEC 61125 Method C.

In an aspect, when the oil of the dielectric fluid is a synthetic esteroil, the metal passivator is present in amount sufficient to control thedissipation value of the dielectric fluid as determined by IEC 60247(120° C.) at or below 0.90 (90%) at 164 hours of oxidative stabilitytesting as evaluated in accordance with by IEC 61125 Method C.

In an aspect, when the oil of the dielectric fluid is a synthetic esteroil, the metal passivator is present in amount sufficient to control thedissipation value of the dielectric fluid as determined by IEC 60247(120° C.) at or below 1.0 (100%) at 164 hours of oxidative stabilitytesting as evaluated in accordance with by IEC 61125 Method C.

In an aspect, when the oil of the dielectric fluid is a bio-sourced oil,the metal passivator is present in amount sufficient to control thedissipation value of the dielectric fluid as determined by IEC 601125(120° C.) at or below 0.50 (50%) at 48 hours of oxidative stabilitytesting as evaluated in accordance with by IEC 61125 Method C.

In an aspect, when the oil of the dielectric fluid is a mineral oil, themetal passivator is present in amount sufficient to control thedissipation value of the dielectric fluid as determined by IEC 60247(120° C.) at or below 0.50 (50%) at 500 hours of oxidative stabilitytesting as evaluated in accordance with by IEC 61125 Method C.

In an aspect, the dielectric fluid components of oil selection,phosphite compounds, optional non-phosphite antioxidant components, andoptional metal passivator are selected to provide specific physicalproperties as follows:

In an aspect, when the oil of the dielectric fluid is a bio-sourced oilor a synthetic ester oil, the dielectric fluid has a Flash Point ofgreater than 250° C. as determined by ISO 2719. In an aspect, when theoil of the dielectric fluid is a bio-sourced oil or a synthetic esteroil, the dielectric fluid has a Flash Point of greater than 270° C. asdetermined by ISO 2719. In an aspect, when the oil of the dielectricfluid is a mineral oil, the dielectric fluid has a Flash Point ofgreater than 135° C. as determined by ISO 2719.

In an aspect, the dielectric fluid has a Fire Point of greater than 300°C. as determined by ISO 2592. In an aspect, the dielectric fluid has aFire Point of greater than 310° C. as determined by ISO 2592.

In an aspect, the dielectric fluid has a Pour Point of less than −5° C.as determined by ISO 3016. In an aspect, the dielectric fluid has a PourPoint of less than −10° C. as determined by ISO 3016. In an aspect, thedielectric fluid has a Pour Point of less than −20° C. as determined byISO 3016. In an aspect, the dielectric fluid has a Pour Point of lessthan −25° C. as determined by ISO 3016. In an aspect, the dielectricfluid has a Pour Point of less than −30° C. as determined by ISO 3016.In an aspect, the dielectric fluid has a Pour Point of less than −45° C.as determined by ISO 3016. In an aspect, when the oil of the dielectricfluid is a bio-sourced oil or a synthetic ester oil, the dielectricfluid has a Pour Point of less than −10° C. as determined by ISO 3016.In an aspect, when the oil of the dielectric fluid comprises a soybeanbased oil, the dielectric fluid has a Pour Point of less than −15° C. asdetermined by ISO 3016, or has a Pour Point of less than −20° C. asdetermined by ISO 3016. In an aspect, when the oil of the dielectricfluid comprises a rapeseed based oil, the dielectric fluid has a PourPoint of less than −30° C. as determined by ISO 3016. In an aspect, whenthe oil of the dielectric fluid is a synthetic ester oil, the dielectricfluid has a Pour Point of less than −45° C. as determined by ISO 3016.In an aspect, when the oil of the dielectric fluid is a mineral oil, thedielectric fluid has a Pour Point of less than −40° C. as determined byISO 3016, or has a Pour Point of less than −60° C. as determined by ISO3016.

In an aspect, the dielectric fluid has a Water Content of less than 750mg/kg as determined by IEC 60814. In an aspect, the dielectric fluid hasa Water Content of less than 200 mg/kg as determined by IEC 60814. In anaspect, the dielectric fluid has a Water Content of less than 100 mg/kgas determined by IEC 60814. In an aspect, the dielectric fluid has aWater content of less than 60 mg/kg as determined by IEC 60814. In anaspect, the dielectric fluid has a Water content of less than 50 mg/kgas determined by IEC 60814. In an aspect, the dielectric fluid has aWater content of less than 30 mg/kg as determined by IEC 60814. In anaspect, the dielectric fluid has a Water content of less than 25 mg/kgas determined by IEC 60814. In an aspect, the dielectric fluid has aWater content of less than 20 mg/kg as determined by IEC 60814. In anaspect, the dielectric fluid has a Water content of from about 5 to 25mg/kg as determined by IEC 60814.

In an aspect, the dielectric fluid has a color of less than 200 Hazen asdetermined by ISO 2211.

In an aspect, the dielectric fluid has a density of less than 1000kg/dm³ at 20° C. as determined by 3675, ISO 12185.

In an aspect, the dielectric fluid has a Kinematic viscosity of fromabout 1 to 15 mm²/s at 100° C., or has a Kinematic viscosity of fromabout 1 to 35 mm²/s at 40° C., or has a Kinematic viscosity of fromabout 20 to 35 mm²/s at 40° C., or has a Kinematic viscosity of fromabout 100 to 3000 mm²/s at −20° C. as determined by ISO 3104. In anaspect, the dielectric fluid comprises mineral oil and has a Kinematicviscosity of from about 3 to 12 mm²/s at 40° C. In an aspect, thedielectric fluid comprises bio-sourced oil and has a Kinematic viscosityof from about 9 to 50 mm²/s at 40° C. In an aspect, the dielectric fluidcomprises vegetable oil and has a Kinematic viscosity of from about 9 to50 mm²/s at 40° C. In an aspect, the dielectric fluid comprisessynthetic oil and has a Kinematic viscosity of from about 7 to 40 mm²/sat 40° C.

In an aspect, the dielectric fluid has an acidity of less than 0.06 mgKOH/g as determined by AOCS Method Cd-63. In an aspect, the dielectricfluid has an acidity of less than 0.03 mg KOH/g as determined by AOCSMethod Cd-63. In an aspect, the dielectric fluid has an acidity of lessthan 0.02 mg KOH/g as determined by AOCS Method Cd-63. In an aspect,when the oil of the dielectric fluid is a mineral oil, the dielectricfluid has an acidity of less than 0.01 mg KOH/g as determined by AOCSMethod Cd-63.

In an aspect, the dielectric fluid has a Breakdown voltage of greaterthan or equal to 35 kV as determined by IEC 60156. In an aspect, thedielectric fluid has a Breakdown voltage of greater than 45 kV asdetermined by IEC 60156. In an aspect, the dielectric fluid has aBreakdown voltage of greater than 55 kV as determined by IEC 60156. Inan aspect, the dielectric fluid has a Breakdown voltage of greater than65 kV as determined by IEC 60156. In an aspect, the dielectric fluid hasa Breakdown voltage of greater than 75 kV as determined by IEC 60156. Inan aspect, when the oil of the dielectric fluid is a mineral oil, thedielectric fluid has a Breakdown voltage of greater than 30 kV asdetermined by IEC 60156. In an aspect, when the oil of the dielectricfluid is a mineral oil, the dielectric fluid has a Breakdown voltage ofgreater than 70 kV as determined by IEC 60156.

In an aspect, the dielectric fluid has a DC resistivity at 90° C. ofgreater than 2 GΩm as determined by IEC 60156. In an aspect, thedielectric fluid has a DC resistivity at 90° C. of greater than 20 GΩmas determined by IEC 60156.

In an aspect, the dielectric fluid is used in a device that is anelectrical system requiring electrical insulation and cooling. In anaspect, the dielectric fluid acts to both transfer heat from the pointof generation and to insulate the conductive elements, such as wirecoils, from adjacent conductive elements. In an aspect, the dielectricfluid is used in a device that is an electrical network providinginterconnection of electrical components, such as for computing,electrical distribution, generation of power or transformation of power.In an aspect, the dielectric fluid is used in a device that comprises acomponent selected from capacitors; voltage regulators; voltagecompensators; and phase shifters. In an aspect, the dielectric fluid isused in a device selected from liquid insulated electrical apparatus,such as electronic circuits and liquid insulated electrical boards andpanels. In an aspect, the dielectric fluid is used in a device that is aswitchgear. In an aspect, the dielectric fluid is used in a device thatis a data center computer module. In an aspect, the dielectric fluid isused in a device selected from transformers comprising a housing, acore/coil assembly in the housing, wherein the dielectric fluid at leastpartially surrounds the core/coil assembly. In an aspect, the dielectricfluid is used in a device selected from transformers such asautotransformers, generator step down and step up transformers,interconnection transformers, flexible AC transformers, distributiontransformers (pole mounted, pad mounted, vault/underground units,submersible, substation), phase-shifting transformers, static voltagecompensators, HVDC transformers, furnace and other industrialtransformers, traction transformers, and earthing transformers. In anaspect, the dielectric fluid is used in a device selected from reactors,battery banks, and battery systems.

In an aspect, a method of insulating a device that is an electricalsystem requiring electrical insulation and cooling comprisesincorporating of any of the dielectric fluids described herein(including selected dielectric fluids containing specifically identifiedmaterials or components, or amounts of same as described herein) in thedevice that is an electrical system requiring electrical insulation andcooling. In an aspect, the method of insulating a device is carried outon a device that is an electrical network providing interconnection ofelectrical components, such as for computing, electrical distribution,generation of power or transformation of power. In an aspect, the methodof insulating a device is carried out on a device that comprises acomponent selected from capacitors; voltage regulators; voltagecompensators; and phase shifters. In an aspect, the method of insulatinga device is carried out on a device selected from liquid insulatedelectrical apparatus, such as electronic circuits and liquid insulatedelectrical boards and panels. In an aspect, the method of insulating adevice is carried out on a device that is a data center computer module.In an aspect, the method of insulating a device is carried out on adevice selected from transformers comprising a housing, a core/coilassembly in the housing, wherein the dielectric fluid at least partiallysurrounds the core/coil assembly. In an aspect, the method of insulatinga device is carried out on a device selected from transformers such asautotransformers, generator step down and step up transformers,interconnection transformers, flexible AC transformers, distributiontransformers (pole mounted, pad mounted, vault/underground units,submersible, substation), phase-shifting transformers, static voltagecompensators, HVDC transformers, furnace and other industrialtransformers, traction transformers, and earthing transformers. In anaspect, the method of insulating a device is carried out on a deviceselected from reactors, battery banks, and battery systems.

In an aspect, a device that is an electrical system requiring electricalinsulation and cooling is provided that comprises of any of thedielectric fluids described herein (including selected dielectric fluidscontaining specifically identified materials or components, or amountsof same as described herein).

In an aspect, the device is selected from devices comprising a componentselected from capacitors; voltage regulators; voltage compensators; andphase shifters.

In an aspect, the device is selected from liquid insulated electricalapparatus, such as electronic circuits and liquid insulated electricalboards and panels. In an aspect, the device is a data center computermodule. In an aspect, the device is selected from transformerscomprising a housing, a core/coil assembly in the housing, wherein thedielectric fluid at least partially surrounds the core/coil assembly. Inan aspect, the device is selected from transformers such asautotransformers, generator step down and step up transformers,interconnection transformers, flexible AC transformers, distributiontransformers (pole mounted, pad mounted, vault/underground units,submersible, substation), phase-shifting transformers, static voltagecompensators, HVDC transformers, furnace and other industrialtransformers, traction transformers, and earthing transformers. In anaspect, the device is selected from reactors, battery banks, and batterysystems.

EXAMPLES

Procedure: Test fluids used in the present examples, unless otherwiseindicated, are an untreated refined, bleached deodorized (“RBD”) soybeanoil (“SBO”) that is treated with 0.5% weight of reagent for evaluationin the stray gassing test. If necessary to dissolve the reagent, thefluid is warmed under nitrogen. The treated fluid is drawn into a 50 mLsyringe, capped to prevent fluid loss and introduction of air, andplaced in an oven at 80° C. or 120° C. for 48 hours. The syringe isremoved from the oven to cool. The fluid is then tested for dissolvedgases in accordance to ASTM Method D-3612 to determine the level ofstray gassing.

Example 1: Comparison of RBD-SBO Fluid Comprising 0.5% Phosphite Ester(Irgafos 168) with Control Sample

The results of testing for determination of the levels of gassing arepresented in Table 1, below:

TABLE 1 Phosphite Hydrogen % H₂ Ethane % CH₃CH₃ compound (ppm) reduction(ppm) reduction Irgafos 168 158 73.6 14 94.3 None 599 n/a 246 n/aIrgafos 168 = tris-(2,4-di-tert-butylphenyl)phosphite

Discussion of Result

At 80° C., the two gases indicative of thermally induced stray gasdegradation are hydrogen and ethane. A significant reduction in thestray gas release of both gases was observed in the RBD-SBO fluidcomprising phosphite ester as compared to the control.

Example 2: Comparison of RBD-SBO Dielectric Fluids, RBD-SBO DielectricFluids Comprising a Phosphite Compound, and RBD-SBO Dielectric FluidsComprising Non-Phosphite Compound Antioxidants

Non-control compositions all contained 0.5 wt. % of the identifiedadditive (either the phosphite compound or the non-phosphiteantioxidant). The RBD-SBO dielectric fluids of this example had aperoxide value of 10.

The results of testing for determination of the levels of gassing arepresented in Table 2, below:

TABLE 2 Hydrogen % H₂ Ethane % CH₃CH₃ Additive/Antioxidant (ppm)reduction (ppm) reduction SAMPLE A (CONTROL) 599 n/a 246 n/a Noantioxidant SAMPLE B tris-(2,4-di-tert- 158 73.6 14 94.3butylphenyl)phosphite (Irganox 168) SAMPLE C (COMPARATIVE) 296 50.6 20516 2,4-Bis(dodecylthiomethyl)- 6-methylphenol SAMPLE D (COMPARATIVE) 49217.9 506  2X increase 2,6-Di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin- 2-ylamind)phenol SAMPLE E (COMPARATIVE)534 10.9 274 11.4% increase Thiodiethylene bis[3- (3,5-di-tert-butyl-4-hydroxyphenyl)propionate] SAMPLE F (COMPARATIVE) 537 10.4 678  2.8Xincrease Benzenamine, N-phenyl-, reaction products with2,4,4-trimethylpentene SAMPLE G (COMPARATIVE) 544 9.2 299 21.5% increaseBenzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)- 4-hydroxy-, methylester SAMPLE H (COMPARATIVE) 552 7.8 232 5.7 Irganox L55 (diphenylalkylamine) SAMPLE I (COMPARATIVE) 754 25.9% increase 134 54.5 Didodecyl3,3′- thiodipropionate SAMPLE J (COMPARATIVE) 497 17 236 4.1Benzenepropanoic acid, 3-(2H-benzotriazol-2-yl)- 5-(1,1-dimethylethyl)-4-hydroxy-, C7-9-branched and linear alkyl esters SAMPLE K (COMPARATIVE)511 14.7 155 37 Decanedioic acid, bis (2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl) ester SAMPLE L (COMPARATIVE) 568 5.2 28214.6% increase Bis(2,2,6,6,-tetramethyl-4- piperidyl)sebaceate SAMPLE M(COMPARATIVE) 628  4.8% increase 358 45.5% increase3,5,5-Trimethyl-hexanoic acid 2-[2,2,6,6-tetra-methyl-4-(3,5,5-trimethyl- hexanoyloxy)-piperidin- 1-yl]-ethyl esterSAMPLE N (COMPARATIVE) 678 13.2% increase 178 27.62-(2H-Benzotriazol-2-yl)- 4,6-ditert-pentylphenol

Discussion of Results

The dielectric fluid comprising a phosphite compound (SAMPLE B)significantly reduced gassing of both hydrogen and ethane as compared todielectric fluids comprising a non-phosphite antioxidant. It is notablethat phenolic based antioxidants comprising metal passivators (i.e.di-tert-butylphenolbenztriazoles with the additional functionality ofmetal surface inhibition—SAMPLES D, E, F, I, L, M, and N) actuallyexhibit an increase the stray gassing as compared to like compositionswithout the metal passivator.

Generally phosphite esters are considered to be secondary antioxidantswith significantly lower antioxidant strength in relation todi-tert-butylphenolic based antioxidants. Comparison to other classes ofantioxidants demonstrates that the effect of the phosphite ester is morethan just an antioxidant effect. Together with the difference inoxidative stability results, this shows that the mechanism of action ininhibiting the stray gassing is likely to be a mechanism other than theantioxidant property. While not being bound by theory, it is believedthat stray gassing is the result of thermally induced radicaldegradation. Therefore, the phosphite esters are inhibiting the straygassing mechanism in an effective manner. Some degree of stray gasreduction is expected from removal of peroxide. The non-phosphite estermaterials do not effectively reduce both gases, and some materialsincrease the gassing tendency of the oil.

Example 3: Comparison of RBD-SBO Low Peroxide Value Dielectric Fluids,RBD-SBO Low Peroxide Value Dielectric Fluids Comprising a PhosphiteCompound, and RBD-SBO Low Peroxide Value Dielectric Fluids ComprisingNon-Phosphite Compound Antioxidants

Non-control compositions all contained 0.5 wt. % of the identifiedadditive (either the phosphite compound, the non-phosphite antioxidantor other additive types). The RBD-SBO dielectric fluids of this examplehad a peroxide value of 0.6.

The results of testing for determination of the levels of gassing arepresented in Table 3, below:

TABLE 3 Additive Chemical name and Hydrogen % Ethane % commercial nameH2 reduction ethane reduction SAMPLE A (CONTROL) 26 n/a 191 n/a nonePhosphite compounds: SAMPLE B 8 69% 4 98% tris-(2,4-di-tert-butylphenyl)phosphite - Irgafos 168 SAMPLE C 4 85% 1 99%2,4,8,10-tetraoxa-3,9-diphos- phaspiro[5.5]undecane,3,9-bis[2,6-bis(1,2- dimethylethyl)-4- methylphenoxy]- ADK STAB PEP-36SAMPLE D 15 42% 3 98% 1,3,7,9-tetratert-butyl- 11-(2-ethylhexoxy)-5H-benzo[d][1,3,2]benzo- dioxaphosphocine ADK STAB HP-10 SAMPLE E 19 27% 199% 2,2-Bis[[3-(dodecylthio)-1- oxopropoxy]methyl]propane- 1,3-diylbis[3- (dodecylthio)propionate] - ADK STAB AO-412S SAMPLE F 12 54% 1 99%4,4′-Isopropylidenediphenol C12-15 alcohol phosphite - ADK1500 SAMPLE G14 46% 2 99% diphenyl isodecyl phosphite- ADK Stab 135A SAMPLE H 13 50%3 98% triisodecyl phosphite- ADK Stab 3010 SAMPLE I 15 42% 2 99%tris(nonylphenyl)phosphite- ADK Stab 1178 SAMPLE J 10 62% 5 97%tris(nonylphenyl)phosphite- Doverphos highpure 4 SAMPLE K 89 242% 20 90%3,9-Bis(octadecyloxy)- increase 2,4,8,10-tetraoxa-3,9-diphos-phaspiro[5.5]undecane- ADK STAB PEP-8 di-tert-butyl phenolicantioxidants: SAMPLE L 22 15% 211 10% (COMPARATIVE) increase Phenol,4,4′,4″-(1- methyl-1-propanyl-3- ylidene)tris [2-(1,1-diemthylethyl)-5-methyl- ADK STAB AO-30 SAMPLE M 49 88% 311 63%(COMPARATIVE) increase increase 2,4,6-Tris(3′,5′- di-tert-butyl-4′-hydroxybenzyl)mesitylene- ADK STAB AO-330 SAMPLE N 156 500% 306 60%(COMPARATIVE) increase increase pentaerythritol tetrakis(33-(3,5-di-tert-butyl- 4-hydroxyphenyl)proprionate- Irganox L101 SAMPLE O30 15% 2 99% (COMPARATIVE) increase hexamethylene bis[3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate]- Irganox 1726 SAMPLE P33 27% 242 27% (COMPARATIVE) increase increase 2,6-di-tert-butyl-4-(4,6-bis(octylthio)- 1,3,5-triazin-2-ylamino) phenol- Irganox 565 SAMPLEQ 47 81% 197 3% (COMPARATIVE) increase increase Thiodiethylene bis[3-[3,5-di-tert-butyl-4- hydroxyphenyl]propionate]- Irganox 1035 SAMPLE R1616 6115% 376 97% (COMPARATIVE) increase increase2-(2H-benzotriazol-2-yl)- 2,4-di-tert-pentylphenol Tinuvin 328 Otheradditive types: SAMPLE S 80 208% 17 91% (COMPARATIVE) increaseBenzamide, 2-hydrooxy- N-1H-1,2,3-triazol-3-yl ADK STAB CDA-1 SAMPLE T54 108% 155 19% (COMPARATIVE) increase Benzenamine, N-phenyl, reactionproducts with 2,4,4-trimethylpentene Irganox L57 SAMPLE U 59 127% 15718% (COMPARATIVE) increase alkylated amine (composition unknown) IrganoxL55 SAMPLE V 62 138% 3 98% (COMPARATIVE) increase dodecyl3-(3-dodecoxy-3- oxopropyl)sulfanylpropanoate (or dilaurylthiodipropianate) Irganox P5800FL SAMPLE W 93 258% 70 63% (COMPARATIVE)increase Decanedioic acid, bis(2,2,6,6- tetramethyl-1-(octyloxy)-4-piperidinyl)ester Tinuvin 123 SAMPLE X 30 15% 269 41% (COMPARATIVE)increase increase Bis(2,2,6,6-tetramethyl-4- piperidyl)sebaceate Tinuvin770 DF SAMPLE Y 47 81% 265 39% (COMPARATIVE) increase increase12H-dibenzo[d,g] [1,3,2]dioxaphocin,2,4,8,10-tetrakis(1,1-dimethylethyl)- 6-hydroxy-,6-oxide, sodium salt¹ ADK STABNA-11 ¹Incorporated to limit of solubility, which is less than 0.5 wt.%.

Discussion of Results

The dielectric fluid comprising a phosphite compound (SAMPLES B-J)significantly reduced gassing of both hydrogen and ethane as compared todielectric fluids comprising a non-phosphite antioxidant. SAMPLE Kexhibited an increase in hydrogen gassing, but a decrease of ethanegassing. However, this data is based on only a single experimental run,and it is believed that the integrity of the phosphite sample may havebeen compromised.

In contrast, the low peroxide value dielectric fluids comprisingdi-tert-butyl phenolic antioxidants or other types of additivesincreased both hydrogen and ethane gassing. This test establishes thatincorporation of phosphite compounds prevents gassing in dielectricfluids when other additives do not prevent gassing in like dielectricfluids that do not contain a phosphite component.

In all subsequent examples, RBD—refined, bleached, deodorized vegetableoil, or synthetic ester oils, are purified by clay treatment before useto obtain dielectric grade fluids. Stray gassing tests are run byholding the air saturated oils in an oven at either 80° C. or 120° C.for either 48 hours or 168 hours, as noted.

Example 4: Effectiveness of Phosphites in Controlling Stray Gassing at80° C. (48 Hour Test) in Comparison to Other Stabilizers, Antioxidants,Passivators

Table 4 demonstrates how RBD soybean oil that has been heated to 80° C.for 48 hours is affected by various additives. The primary indicatorsare hydrogen and ethane. Levels of other gases are insignificant inthese examples. Sample 4-1 is the RBD-SBO without additives and thermaltreatment to compare the base level of stray gases, analyzed bydissolved gas analysis (DGA). Sample 4-2 is RBD-SBO without additivesafter thermal treatment. Out of all of the classes of antioxidantstested, the phosphite compound shows a significant reduction in both ofthe stray gases. The other examples show either no significant change,or an increase in either or both stray gases.

TABLE 4 Initial data demonstrating effectiveness of phosphites incontrolling stray gassing at 80° C. (48 hour test) in comparison toother stabilizers, antioxidants, passivators, etc. RBD-SBO was used with0.5% weight of additive. Sample Hydrogen Ethane Number Antioxidant AOClass (ppm) (ppm) 4-1 RBD-SBO, No additives 50 14 Not heated 4-2RBD-SBO, No additives 599 246 heated 4-3 Irgaphos 168 Phosphite 158 194-4 Irganox L55 Alkylated amine 552 232 (diphenylamine basedantioxidant) 4-5 Irganox thiosynergist 754 134 PS800FL (peroxidedecomposer) 4-6 TInuvin 249 HALS (hindered 628 358 amine lightstabilizer) 4-7 Irganox 1035 DTBP (di-tert- 534 274 butylphenol) derivedantioxidant 4-8 Tinuvin HALS 568 282 770 DF 4-9 Irganox L57 Aryl amine537 687 antioxidant 4-10 Tinuvin Hydroxyphenyl- 678 178 328-2benzotriazole (antioxidant and passivator) 4-11 Irganox 1726 Thiomethyl296 205 phenol antioxidant 4-12 Irganox 565 DTPB amine 492 506 triazinealkyl sulfide AO 4-13 Irganox L135 DTPB methyl ester 544 299 4-14Tinuvin 123 HALS amino-ether 511 155 4-15 Tinuvin Hydroxyphenyl- 497 236384-2 benzotriazole (AO + passivator + UV protectant

From this data, it is apparent that butylated phenol antioxidants do notcontrol stray gassing, but can contribute to a significant increase ofstray gassing in bio-sourced oils. Passivator compounds, which aregenerally benzotriazole compounds (Examples 4-10, 4-12 and 4-15), alsosignificantly increase stray gassing in bio-sourced oils.

Example 5: Negative Interactions of the Butylated Phenol, Irganox L101and the Passivator

The interaction of one of the most common antioxidants used intransformer oils, Irganox L101 (butylated phenol class), and the mostcommon passivator, Irgamet 39, is shown in contrast or in conjunctionwith the phosphite compound Irgaphos 168 in Table 5.

TABLE 5 The Negative Interactions of the Butylated Phenol, Irganox L101and the Passivator Irgamet 39, Against the Compensating Impact ofIrgaphos 168 Phosphite on Controlling Stray Gassing in RBD-SBO at 80° C.for 48 hours. Irgaphos Irganox Irgamet Sample 168 L101 39 HydrogenEthane Number % wt. % wt. ppm ppm ppm 5-16 0 0 0 15 316 5-17 0 0.4 0 56325 5-18 0.4 0 0 <2 <1 5-19 0.2 0.4 0 6 <1 5-20 0.4 0.8 0 4 8 5-21 0 0100 516 23 5-22 0 0.4 100 228 128 5-23 0 0.8 400 216 45 5-24 0.4 0 40066 6 5-25 0.4 0.2 400 56 4 5-26 0.2 1.0 100 25 4 5-27 0.8 0.6 100 15 25-28 0.8 1.0 100 14 2

Comparison of Samples 5-16 and 5-17 demonstrates that incorporation ofthe traditional butylated phenol increases the stray gassing over thatof purified soybean oil by increasing the release of hydrogen by 370%.In contrast, comparison of Samples 5-16 and 5-18 demonstratessignificant reduction of the stray gassing by the use of phosphitecompounds, even reducing the levels below that of the purified,untreated oil. Samples 5-19 and 5-20 demonstrate that the phosphitecompounds even reverse the stray gassing effect of the butylated phenol.Samples 5-20, 5-21, and 5-22 show the negative impact of passivator onoils, where a small amount of passivator has a severe detrimental effecton stray gassing on the oils. Samples 5-24 through 5-28 demonstrate howthe Irgaphos 168 phosphite compound overcomes the stray gassing effectsof the combination of butylated phenol antioxidant and benzotriazolepassivator.

Example 6: Effect of Typical Antioxidants in Increasing the Stray Gases

The general behavior of typical antioxidants in increasing the straygases is demonstrated in Table 6. These compounds are classified asbutylated phenols, di-t-butyl phenolic thiotriazine, di-t-butylphenolicmercaptan, di-t-butyl phenolic benzotriazine, aminotriazole, benzamines,mercaptan diester, piperidinyl ester-N-alkoxide piperidinyl ester

TABLE 6 Increase of Stray Gases in RBD-SBO at 80° C. for 48 hours fromthe Use of 0.5% Weight Antioxidant. Hydrogen Increase Ethane IncreaseAntioxidant Chemical Name (ppm) (%) (ppm) (%) None Control 26 n/a 191n/a AO-30 Phenol, 4,4′,4″-(1-methyl-1- 22 −15% 211 10%propanyl-3-ylidene)tris[2-(1,1- increase diemthylethyl)-5-methyl- AO-3302,4,6-Tris(3′,5′-di-tert-butyl-4′- 49 88% 311 63%hydroxybenzyl)mesitylene increase increase Irganox L101 pentaerythritoltetrakis(33- 156 500% 306 60% (3,5-di-tert-butyl-4- increase increasehydroxyphenyl)proprionate Irganox 1726 hexamethylene bis[3-(3,5-di- 3015% 2 −99% tert-butyl-4- increase hydroxyphenyl)propionate] Irganox 5652,6-di-tert-butyl-4-(4,6- 33 27% 242 27% bis(octylthio)-1,3,5-triazin-2-increase increase ylamino) phenol Irganox 1035 Thiodiethylenebis[3-[3,5-di- 47 81% 197 3% tert-butyl-4- increase increasehydroxyphenyl]propionate] Tinuvin 328 2-(2H-benzotriazol-2-yl)-2,4- 16166115% 376 97% di-tert-pentylphenol increase increase CDA-1 Benzamide,2-hydrooxy-N-1H- 80 208% 17 −91% 1,2,3-triazol-3-yl increase Irganox L57Benzenamine, N-phenyl, 54 108% 155 −19% reaction products with 2,4,4-increase trimethylpentene Irganox L55 alkylated amine (trade secret) 59127% 157 −18% increase Irganox P5800FL dodecyl 3-(3-dodecoxy-3- 62 138%3 −98% oxopropyl)sulfanylpropanoate increase (or dilaurylthiodipropianate) Tinuvin 123 Decanedioic acid, bis(2,2,6,6- 93 258% 70−63% tetramethyl-1-(octyloxy)-4- increase piperidinyl)ester Tinuvin 770DF Bis(2,2,6,6-tetramethyl-4- 30 15% 269 41% piperidyl)sebaceateincrease increase NA-11 12H-dibenzo[d,g][1,3,2]di- 47 81% 265 39%oxaphocin,2,4,8,10-tetrakis(1,1- increase increasedimethylethyl)-6-hydroxy-,6-oxide, sodium salt

Example 7: Reduction of Stray Gassing in Oil by Phosphite Compounds

A screening of phosphite compounds demonstrates the generality of theability of these compounds to reduce stray gassing in oils.

Table 7 demonstrates the benefits of treating purified, refined,bleached, deodorized soybean oil with 0.5% of the listed phosphite, thenheating the in a sealed container for 48 hours at 80° C., then testingthe oil for dissolved gases.

TABLE 7 Screening of Phosphite Compounds for Reduction of Stray Gassingin RBD-SBO at 80° C. for 48 hours. Hydrogen % Ethane % PhosphiteChemical Name ppm reduction ppm reduction None Control 26 n/a 191 n/aIrgafos 168 tris-(2,4-di-tert- 8 69% 4 98% butylphenyl)phosphite PEP-362,4,8,10-tetraoxa-3,9- 4 85% 1 99% diphosphaspiro[5.5]undecane,3,9-bis[2,6- bis(1,2-dimethylethyl)- 4-methylphenoxy]- TriphenylTriphenyl Phosphite <1 97% 3 99% phosphite HP-101,3,7,9-tetratert-butyl- 15 42% 3 98% 11-(2-ethylhexoxy)-5H-benzo[d][1,3,2]benzo- dioxaphosphocine AO-412S 2,2-Bis[[3- 19 27% 1 99%(dodecylthio)-1-oxopro- poxy]methyl]propane- 1,3-diyl bis [3-(dodecylthio)propionate] ADK1500 4,4′- 12 54% 1 99%Isopropylidenediphenol C12-15 alcohol phosphite ADK Stab diphenylisodecyl 14 46% 2 99% 135A phosphite ADK Stab triisodecyl phosphite 1350% 3 98% 3010 ADK Stab tris(nonylphenyl)phosphite 15 42% 2 99% 1178Doverphos tris(nonylphenyl)phosphite 10 62% 5 97% highpure 4

Example 8: Comparison of Butylated Phenol with Phosphite Compound inHighly Purified RBD-SBO for 18 Hours at 80° C. and 120° C.

Stray gassing of Highly Purified RBD-SBO containing either a butylatedphenol, Irganox L101, or a phosphite compound, Irgaphos 168, wascompared when the oil was held for 18 hours at 80° C. or 120° C. Resultsare shown in Table R

TABLE 8 Comparison of Stray gassing of Highly Purified RBD-SBOcontaining either a butylated phenol or a phosphite compound IrgaphosIrganox Sample Temperature 168 L101 Hydrogen Ethane Number ° C. WT. %Wt. % ppm ppm 8-1 80 0 0.4 43 95 8-2 80 0.4 0 6 8 8-3 120 0 0.4 44 3478-4 120 0.4 0 30 85

Example 9: Evaluation of Stray Gassing of Aliphatic Synthetic EsterCompositions Comprising Benzotriazole Passivator And Phosphite AtVarious Levels

Temperatures of 120° C. are known to accelerate natural and syntheticester degradation. This was verified with untreated mineral oil andsynthetic ester at 80° C. in the oven test where the higher stability ofaliphatic based oils was demonstrated with the lack of stray gassing.The increased stability of the aliphatic compounds requires temperaturesabove 100° C. to increase the rate of stray gassing. Samples were testedfor both 48 hours and 168 hours at 120° C. Table 9A demonstrates resultsafter 48 hours of thermal treatment at 120° C.

TABLE 9A Stray Gassing of Aliphatic Synthetic Ester at 120° C. for 48Hours and Stabilizing Effect of Irgaphos 168 Phosphite. Irgaphos IrganoxIrgamet Sample 168 L101 39 Hydrogen Ethane Number wt. % wt. % ppm ppmppm Midel 7131 0 Level Level 81 317 unknown unknown 9-29 0 0 0 57 829-30 0 0.4 0 13 <1 9-31 0 0.4 400 329 <1 9-32 0.4 0 400 <2 <1 9-33 0.40.4 400 5 72

The commercial synthetic ester sample Midel 7131, known to have IrganoxL101 and passivator at undetermined levels, shows high levels of straygassing within the shorter time period than the synthetic ester fluidused in this study. At the elevated temperatures where butylated phenolsare known to act more rapidly toward peroxide induced stray gassing(compare sample 9-29 and 9-30), the effect of benzotriazole passivatoris shown to overcome any effect of the butylated phenol andsignificantly increase the hydrogen stray gases (sample 9-31). Thephosphite compound, Irgaphos 168, significantly reduces the hydrogenstray gassing in the synthetic ester in samples 9-32 and 9-33.

Increasing the severity of the exposure by extending the time to 168hours at 120° C. (Table 9B) demonstrates the superiority of thephosphite compound in controlling stray gassing under the challenge ofother additives.

TABLE 9B Stray Gassing of Aliphatic Synthetic Ester at 120° C. for 168Hours and Stabilizing Effect of Irgaphos 168 Phosphite. Irgaphos IrganoxIrgamet Sample 168 L101 39 Hydrogen Ethane Number wt. % wt. % ppm ppmppm 9-34 0 0 0 135 58 9-35 0 0.4 400 228 <1 9-36 0.4 0 400 <2 <1 9-370.4 0.2 400 <2 <1 9-38 0.4 0.4 400 <2 <1

Example 10: Demonstration of Irgaphos 168 Phosphite Compound inPreventing Stray Gassing in Mineral Oil

Temperatures of 120° C. are known to degrade mineral oils. Table 10demonstrates the high rate of stray gassing in a mineral oil fluidwithout additives, and the ability of phosphite compound to preventstray gassing.

TABLE 10 Demonstration of Irgaphos 168 phosphite compound in preventingstray gassing in mineral oil. Sample Irgaphos Hydrogen Methane EthaneEthylene Number 168 wt. % ppm ppm ppm ppm 10-39 0 31 444 413 14 10-400.4 <2 4 <1 2

Example 11: Oxidative Stability Test Results on RBD-SBO with and WithoutPhosphite and Passivator

Oxidative stability testing of the soybean oil formulations (Table 11)indicates that Irgaphos 168 can be used in formulations with improvementin total acidity (specification<0.3 total). However, the use ofpassivator with bio-sourced oils has been found to significantlyincrease viscosity and acidity of the fluids. In the case of aliphaticsynthetic esters, passivator does not affect viscosity, but has adetrimental effect on acidity and dissipation factor (tan 8) of thefluids as demonstrated in Table 12.

TABLE 11 Oxidative Stability Test Results on RBD-SBO (IEC 61125 MethodC, 48 hrs, 120° C., 2.5 mL/min air flow). Total acids Viscosity tandelta Irgaphos Irganox Irgamet mg KOH/g Increase % (90^(°) C.) 168 L10139 (spec. ≤ (spec. ≤ (spec. ≤ wt. % wt. % ppm 0.3) 30%) 0.5) 0 0 0 0.29221.5% 0.03719 0.4 0 0 0.026 21.8% 0.03267 0.4 0.2 0 0.132 24.2% 0.078500.4 0.2 200 0.279 33.9% 0.17850

Example 12: Oxidative Stability Test Results on Aliphatic SyntheticEster

Aliphatic synthetic ester fluid formulated with the Irgaphos 168phosphite compound shows superior properties in the oxidative stabilitytest. Viscosities remain unchanged when using Irgaphos 168, and theresults of testing after 800 hours of oxidative stability testing at120° C. with according to IEC 61125, Method C, at a 2.50 mL/min flow ofair, exceeds the specifications required for the 164 hour test. Resultsare summarized in Table 12.

TABLE 12 Oxidative Stability Test Results on Aliphatic Synthetic Ester(IEC 61125 Method C, 120° C., 2.5 mL/min air flow, at the specifiedtimes of 164 or 800 hours). Test Duration Total acids tan delta ColorIrgaphos 168 Irganox L101 Irgamet 39 (hours) mg KOH/g (90° C.) (Hazen)wt. % wt. % ppm (spec = 164) (spec. ≤ 0.3) (spec. ≤ 0.5) (<200) 0.25 0400 200 8.061 0.1175 62.3 0.25 0 200 200 1.0273 0.0815 85 0.4 0 200 2000.185 0.0393 101 0.5 0 200 200 0.1136 0.0788 356 0.5 0 400 200 0.1420.0284 97 0.2 0.2 400 164 0.0840 0.0325 103 0.5 0.2 400 164 0.08380.0325 103 0.5 0.2 400 164 0.1133 0.0514 123 0.5 0 400 164 0.0849 0.1308426 0.2 0.2 0 800 0.1215 2.58 >1000 0.5 0 400 800 0.2102 0.0642 354 0.50 400 800 0.1343 0.0945 317 Note: Viscosity change in all cases is<1.0%, and sludge is <0.01% weight.

Example 13: Reduction of Stray Gassing in Natural Oils Having HighPeroxide Values

Oils having high initial peroxide content also exhibit increased straygassing, as is seen in Table 13. However, this stray gassing issignificantly reduced by the use of the Irgaphos 168 phosphite compound.It is noted that the presence of a conventional antioxidant(non-phosphite antioxidant component) does not prevent formation ofperoxide, but instead acts to degrade peroxides after the peroxide isformed. However, the conventional antioxidant will not effectivelyreduce peroxide buildup at ambient temperature. Elevated temperature iseffective at increasing the interaction between the conventionalantioxidant and peroxide, but also increases the rate of thermaldegradation of the oil.

TABLE 13 High Peroxide Value oils and the effect of Irganox 168 toreduce stray gassing (48 hours, 80° C.), Example Peroxide Irgaphos 168Irganox L101 Irgamet 39 Hydrogen Ethane Number Oil Number % wt. % wt. %wt. ppm ppm 13-16 RBD-SBO <1 0 0 0 15 316 13-41 RBD-SBO 20 No heat 0 0 0182 (no heat) 15 (no heat) 13-42 RBD-SBO 20 0 0 0 1391 294 13-43 RBD-SBO24 0.4 0 0 22 16 13-44 Sunflower 46 0 0.4 100 3778 12 13-45 Sunflower 460.4 0 100 635 180 13-46 US Canola 73 0 0.4 110 11089 2295 13-47 USCanola 73 0.4 0 110 635 1808

Example 14: Reduction of Stray Gassing in Natural Oils Having Low LowPeroxide Content

Experiments were carried out showing reduction of stray gassing innatural oils that do not have high peroxide content. Test results areprovided in Tables 14-1 and 14-2.

TABLE 14-1 Effectiveness of Irganox 168 at Reducing Stray Gassing inBio-Sourced Oils at 80° C. for 48 hours. Sample Irgaphos 168 IrganoxL101 Irgamet 39 Hydrogen Ethane Number Oil Type wt. % wt. % ppm ppm ppm14-1 High Oleic Canola 0 0.4 0 132 17 14-2 High Oleic Canola 0.4 0 0 175 14-3 US Canola 0 0.4 100 294 69 14-4 US Canola 0 0.4 0 61 45 14-5 USCanola 0.4 0 100 6 12 14-6 US Canola 0.4 0 0 6 <1 14-7 Sunflower 0 0 200282 <1 14-8 Sunflower 0.4 0 200 7 <1 14-9 Sunflower 0.4 0.35 0 <2 <114-10 Sunflower 0.4 0.35 200 <2 <1 14-11 EU Rapeseed 0 0.4 0 50 44 14-12EU Rapeseed 0.4 0 0 6 9

TABLE 14-2 Examples of the Phosphite Compound, Triphenyl Phosphite, onvarious oils AT 80° C. for 48 Hours. Sample P(OPh)₃ Irganox L101 Irgamet39 Hydrogen Ethane Number Oil Type wt. % wt. % ppm ppm ppm 14-13 HighOleic Canola 0 0.4 100 2591 170 14-14 High Oleic Canola 0.4 0 0 2 1514-15 EU Rapeseed 0.4 0 0 <2 9 14-16 High Peroxide Sunflower 0.4 0 0 113 (PV = 46) 14-17 RBD-SBO 0.4 0 0 <2 3 14-18 US Canola 0.5 0 0 2 15

Example 15: Confirming that Phosphite in Oil Does Not Interfere withTesting of Transformers

It is important that the phosphite compounds do not interfere with thediagnostic testing of transformers, where acetylene levels are used todetermine whether an arcing or electrical discharge situation isoccurring. To test this, the oil was subjected to greater than 65 kV and50 electrical discharges that were sent through a 2 mm gap into 350 mLof oil to demonstrate that there was no difference in the acetylene andDGA levels. It should be noted that this oil was not heat treated, so noadditional stray gases were expected from anything other than the sparkgoing through the oil.

TABLE 15 Demonstration of Non-Interference of Phosphite Compound,Irgaphos 168, on the Electrical Discharge Diagnosis of Bio-Sourced Oil(RBD-SBO). Irgaphos 168 Irgamet 39 Hydrogen Methane Ethane EthyleneAcetylene Wt. % ppm ppm ppm ppm ppm ppm 0 0.4 21 5 1 11 36 0.4 0 20 4 <19 31

As used herein, the terms “about” or “approximately” mean within anacceptable range for the particular parameter specified as determined byone of ordinary skill in the art, which will depend in part on how thevalue is measured or determined, e.g., the limitations of the samplepreparation and measurement system. Examples of such limitations includepreparing the sample in a wet versus a dry environment, differentinstruments, variations in sample height, and differing requirements insignal-to-noise ratios. For example, “about” can mean greater or lesserthan the value or range of values stated by 1/10 of the stated values,but is not intended to limit any value or range of values to only thisbroader definition. For instance, a concentration value of about 30%means a concentration between 27% and 33%. Each value or range of valuespreceded by the term “about” is also intended to encompass theembodiment of the stated absolute value or range of values.Alternatively, particularly with respect to measurements on logarithmicscales such as seen in biological systems or processes, the term canmean within an order of magnitude, preferably within 5-fold, and morepreferably within 2-fold, of a value.

Throughout this specification and claims, unless the context requiresotherwise, the word “comprise”, and variations such as “comprises” and“comprising”, will be understood to imply the inclusion of a statedinteger or step or group of integers or steps but not the exclusion ofany other integer or step or group of integer or step. When used herein“consisting of” excludes any element, step, or ingredient not specifiedin the claim element. When used herein, “consisting essentially of” doesnot exclude materials or steps that do not materially affect the basicand novel characteristics of the claim. In the present disclosure ofvarious embodiments, any of the terms “comprising”, “consistingessentially of” and “consisting of” used in the description of anembodiment may be replaced with either of the other two terms.

All patents, patent applications (including provisional applications),and publications cited herein are incorporated by reference as ifindividually incorporated for all purposes. Unless otherwise indicated,all parts and percentages are by weight and all molecular weights areweight average molecular weights. The foregoing detailed description hasbeen given for clarity of understanding only. No unnecessary limitationsare to be understood therefrom. The invention is not limited to theexact details shown and described, for variations obvious to one skilledin the art will be included within the invention defined by the claims.

What is claimed is:
 1. A dielectric fluid comprising: a synthetic esteroil comprising a reaction product of a pentaerythritol and a C5-C12linear or branched carboxylic acid; a phosphite component having one tothree aryloxy groups and comprising from 0.1 to 0.5 wt % of thedielectric fluid; a metal passivator; and a phenolic antioxidantcomponent, wherein, the amount of the phosphite component is sufficientto reduce the stray gassing of the dielectric fluid as determined bydissolved gas analysis (ASTM D3612-02, Method C) by at least 60% ascompared to a like dielectric fluid composition that does not contain aphosphite component, wherein the stray gas is hydrogen, and wherein thedielectric fluid has a fire point greater than 300° C. as determined byISO 2592 and has a breakdown voltage of at least 45 kV as determined byIEC
 60156. 2. The dielectric fluid of claim 1, wherein the phosphitecomponent has three aryloxy groups.
 3. The dielectric fluid of claim 1,wherein the phosphite component is selected from the group consisting ofcyclic aryl phosphites, cyclic alkyl-aryl phosphites, aryl cyclicphenoxy phosphites, bis aryl phosphites, alkyl aryl phosphites, andmixtures thereof.
 4. The dielectric fluid of claim 1, wherein thephosphite component is selected from the group consisting oftris-(2,4-di-tert-butylphenyl)phosphite; bis(2,4-di cumylphenylpentaerythritol diphosphite; tris-nonylphenylphosphite;1,3,7,9-tetratert-butyl-11-(2-ethylhexoxy)-5H-benzo[d][1,3,2]benzodioxaphosphocine;3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane;bis(2,4-di-tert-butylphenol)pentaerythritol diphosphite;4,4′-Isopropylidenediphenol C12-15 alcohol phosphite;3,9-diphenoxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane;triphenyl phosphite; isodecyl diphenyl phosphite; 2-ethylhexyl diphenylphosphite; 5,5-dimethy-2-phenoxy-1,3,2-dioxaphosphorinane; methyldiphenyl phosphite; and mixtures thereof.
 5. The dielectric fluid ofclaim 1, wherein the phenolic antioxidant component is selected from thegroup consisting of Pentaerythritoltetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate); Hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate];Octadecyl-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; Ethylenebis(oxyethylene) bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate);2,6-Di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol;N,N′-hexane-1,6-diylbis(3-3,5-di-tert-butyl-4-hydroxyphenylpropionamide);4,6-Bis(octylthiomethyl)-o-cresol; 4,4′-methylene-bis-2,6-di-tert-butylphenol; and 2,6-Di-tert-butyl-4-methylphenol.
 6. A method of insulatingan electrical distribution or power device, comprising incorporating adielectric fluid of claim 1 in the electrical distribution or powerdevice.
 7. An electrical distribution or power device comprising adielectric fluid of claim
 1. 8. The electrical distribution or powerdevice of claim 7, wherein the device is selected from a capacitor and atransformer.
 9. The dielectric fluid of claim 1, wherein the metalpassivator is selected from benzotriazole or its derivatives.
 10. Thedielectric fluid of claim 1, wherein the metal passivator is present inamount sufficient to control the dissipation value of the dielectricfluid at or below 0.50 (50%) at 48 hours of oxidative stability testing.11. The dielectric fluid of claim 1, wherein the metal passivator ispresent in amount of from 0.005 to 1.0% wt.
 12. The dielectric fluid ofclaim 1, wherein the metal passivator is present in an amount of from0.005 to 0.4 wt %.
 13. The dielectric fluid of claim 1, wherein themetal passivator is selected from the group consisting ofN,N-bis(2-ethylhexyl)-ar-methyl-1H-Benzotriazole-1-methanamine;N,N-bis(2-ethylhexyl)-1H-1,2,4-Triazole-1-methanamine; 1H-Benzotriazole;Methyl-1H-benzotriazole; and2,2′-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bis-ethanol.